From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84A152FB61F; Thu, 18 Sep 2025 10:14:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758190472; cv=none; b=Cy37h40hG0gq2IRC+tx4kXyFQXRn6e4mH3xGVT2XCnah2RUVqy3sZVD3zJ9dJGz88WRSboF59BJiNRJ8WFbe5Yu2tjyBsydGpWtZMBpU8TmDTxEbuHjOuSfFjVvPi7daj7SQFTU+l4+TO2b1KNjpN/+oDAEFxKEBRgEU6wEJuYA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758190472; c=relaxed/simple; bh=sx/aMTOwkIm8Zaz1kuQ2mUJmqtZSUqCr6SzbEBFIuVw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=pOGrQqjPGaooeBEerDSKDmBhU/3JOG+SYHH4CGP+ALBGcuCD6wdkVqUBxCkTbJQsFq6N2vjfyXHL5I0UMSusWAUgtjTX6zJ/5ExbINtPk7pacmnCHCZpCmBILvmVGPN5siqCR6NpBCrt9T/gxDvy2cbkxNGAA9uDN/aweA6UCys= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z5deEj++; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z5deEj++" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 39C79C4CEF0; Thu, 18 Sep 2025 10:14:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758190472; bh=sx/aMTOwkIm8Zaz1kuQ2mUJmqtZSUqCr6SzbEBFIuVw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z5deEj++9GSLDEff9ZH/GhmPKjf3zNL366uhfQCbhYow4a2xuEFODAPAXDGZ12rjQ rI8uwsx9QF55Vy/lIvY8KcJaxg7aFNH4qLethQIcS+4kAjD4j3+TmS6IMwo880wAs6 p9l6CB8stblPXSSt5YNvKFlZdvHN2qrhp//K6slFzp/Cd/zxc4NR/IXlD1z+osOk3+ m6ku1kaIRCH66DmwkDDNcfFVrKlTjPhIcVFPTvCjzrShyPtMK3RVO2Zotj1Bpg7x0D xkh8w4JpbUBO+SzDoFarzDdGBpkBz2FG/sRCcJodQnNyYPmrCMwFWJ7MzY5TEcdqXO /5qS2pEQArV5A== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id BD5FDCE0D66; Thu, 18 Sep 2025 03:14:31 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH v2 2/8] doc: Add RCU guards to checklist.rst Date: Thu, 18 Sep 2025 03:14:24 -0700 Message-Id: <20250918101430.2592294-2-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <921eb978-5f39-4480-bcf6-c735f859c694@paulmck-laptop> References: <921eb978-5f39-4480-bcf6-c735f859c694@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Also note that RCU guards can be easier to use. Signed-off-by: Paul E. McKenney --- Documentation/RCU/checklist.rst | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index 7de3e308f330f6..c9bfb2b218e525 100644 --- a/Documentation/RCU/checklist.rst +++ b/Documentation/RCU/checklist.rst @@ -69,7 +69,13 @@ over a rather long period of time, but improvements are always welcome! Explicit disabling of preemption (preempt_disable(), for example) can serve as rcu_read_lock_sched(), but is less readable and prevents lockdep from detecting locking issues. Acquiring a - spinlock also enters an RCU read-side critical section. + raw spinlock also enters an RCU read-side critical section. + + The guard(rcu)() and scoped_guard(rcu) primitives designate + the remainder of the current scope or the next statement, + respectively, as the RCU read-side critical section. Use of + these guards can be less error-prone than rcu_read_lock(), + rcu_read_unlock(), and friends. Please note that you *cannot* rely on code known to be built only in non-preemptible kernels. Such code can and will break, @@ -405,9 +411,11 @@ over a rather long period of time, but improvements are always welcome! 13. Unlike most flavors of RCU, it *is* permissible to block in an SRCU read-side critical section (demarked by srcu_read_lock() and srcu_read_unlock()), hence the "SRCU": "sleepable RCU". - Please note that if you don't need to sleep in read-side critical - sections, you should be using RCU rather than SRCU, because RCU - is almost always faster and easier to use than is SRCU. + As with RCU, guard(srcu)() and scoped_guard(srcu) forms are + available, and often provide greater ease of use. Please note + that if you don't need to sleep in read-side critical sections, + you should be using RCU rather than SRCU, because RCU is almost + always faster and easier to use than is SRCU. Also unlike other forms of RCU, explicit initialization and cleanup is required either at build time via DEFINE_SRCU() @@ -443,10 +451,13 @@ over a rather long period of time, but improvements are always welcome! real-time workloads than is synchronize_rcu_expedited(). It is also permissible to sleep in RCU Tasks Trace read-side - critical section, which are delimited by rcu_read_lock_trace() and - rcu_read_unlock_trace(). However, this is a specialized flavor - of RCU, and you should not use it without first checking with - its current users. In most cases, you should instead use SRCU. + critical section, which are delimited by rcu_read_lock_trace() + and rcu_read_unlock_trace(). However, this is a specialized + flavor of RCU, and you should not use it without first checking + with its current users. In most cases, you should instead + use SRCU. As with RCU and SRCU, guard(rcu_tasks_trace)() and + scoped_guard(rcu_tasks_trace) are available, and often provide + greater ease of use. Note that rcu_assign_pointer() relates to SRCU just as it does to other forms of RCU, but instead of rcu_dereference() you should -- 2.40.1